Apparatus for fixing boiler tubes during replacement of same

ABSTRACT

Apparatus for facilitating removal of spent tubes from boilers or heat exchangers in environments where access to one side of the wall through which the tube extends is limited. The apparatus includes a jaw assembly that is movable between a retracted position, at which it can be introduced within a tube to be removed, and an expanded position, at which it radially expands the tube so as to prevent longitudinal movement of the tube. The jaw assembly can be manipulated between the retracted and expanded positions solely through the tube interior so that a worker stationed at a proximal end of the tube to be removed can move the jaw assembly to the expanded position at which the distal end of the tube is fixed against longitudinal movement. After application of pulling forces to fracture the tube, the jaw assembly can be disengaged solely by access through the tube from the proximal end, whereby efficiency of tube removal in environments of limited access is materially enhanced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to method and apparatus for fixing one end of aboiler tube that is tightly retained in an aperture wall preparatory topulling the tube during replacement thereof.

2. Description of the Prior Art

Tubes of relatively small diameter are widely used in boilers and inheat exchangers to increase the surface area across which heat istransferred during operation of such devices In the case of boilersthere is typically a massive wall, and in heat exchangers there are twoor more tube sheets; these walls or sheets are substantial permanentstructures and are provided with numerous passages through which tubesof relatively small diameter are disposed. The tubes have a life that isshorter than the permanent structures in which they are installed sothat replacement of the tubes at periodic intervals is common practice.

Because the tubes are tightly mounted within the passages, their removalis a non-trivial task. One technique that has been previously employedinvolves gripping the tube and applying sufficient longitudinal force topull the tube from the passage in which it resides. As the tube slidesalong the passage, longitudinal striations are created in the passagesurface; such striations form leak paths after installation of new tubesand consequent degradation of the efficiency of the device. In caseswhere a boiler wall or tube sheet is formed of alloys, pieces of thewall or tube sheet are liable to break away during such pulling so as torequire replacement or extensive repair of the boiler wall or tubesheet.

The foregoing problems resulted in development of a technique thatinvolves clamping the tube at one side of the boiler wall or tube sheet,gripping the other end of the tube, and applying tensile force to thetube. As the tube begins to fail, it elongates and reduces diameter sothat when the tube finally fails in response to the tensile force, itsdiameter is sufficiently small that no damage is done to the portion ofthe boiler wall or tube sheet that defines the aperture or passage inwhich the tube is installed.

Typical practice requires two workers to effect removal of the tubes,one working on each side of the boiler wall or tube sheet. In additionto requiring more manhours, this prior art technique often requiresaccess to virtually unaccessible chambers, in consequence of which greatdifficulty is experienced and the integrity of the portion of the boilerwall that defines the passage is jeopardized.

SUMMARY OF THE INVENTION

According to the present invention a jaw assembly composed of pluralsegments is provided. The jaw assembly can be retracted and expanded ina radial direction. In the retracted position the overall diameter ofthe jaw assembly is such as to fit through a tube so that a workerlocated at the proximal side of a boiler wall can employ an implement topass the jaw assembly through the tube opening and position the jawassembly in alignment with the distal wall of the boiler wall or tubesheet. At such position the jaw assembly is expanded, solely by accessthrough the tube interior in order to fix the distal end of the tube tothe boiler wall or tube sheet. Then a portion of the implement requiredto so expand the jaw assembly is removed, a conventional gripping deviceis threaded into the tube adjacent the proximal side, and pulling bymeans of conventional hydraulic devices or the like can proceed withoutrequiring a worker on the distal side of the boiler wall or tube sheet.After the tube fails in response to the great tensile force appliedthereto, the part of the tube to which the jaw assembly is connected canbe tapped through to the distal side at which it falls to the bottom ofthe volume in which it is contained. The jaw assembly can then be easilyrecovered for reuse.

The principal object of the invention is to provide method and apparatuswhich is capable of fixing a tube at the distal side of a boiler wall ortube sheet by manipulation of the device solely through the centralpassage of the tube. In one form of the invention the jaw assembly ismoved to the retracted position, moved through the tube to the distalside, and then expanded. In another form of the invention, useful whereat least limited access to the distal side can be had, the jaw assemblycan be positioned at the distal side and then engaged and manipulated bya mandrel passed through the tube by a workman on the proximal side ofthe boiler wall or tube sheet.

The foregoing together with other objects, features, and advantages willbe more apparent after referring to the following specification and theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary perspective view of a steam boiler whichillustrates a typical environment in which the invention is particularlyuseful.

FIG. 2 is an exploded view of apparatus according to the invention aswell as known pulling apparatus which forms no part of the invention perse but is shown in the interest of completeness.

FIG. 3 is an elevation view in cross section of apparatus according tothe invention positioned in a tube and disposed in the retractedposition.

FIG. 4 is a view similar to FIG. 3 showing the jaw assembly in anexpanded condition.

FIG. 5 is a view shown with the expansion mandrel removed and a tubewall gripping member, shown in broken lines, in place within the tube.

FIG. 6 is a cross-sectional view taken on line 6--6 of FIG. 5.

FIG. 7 is a view showing the tube immediately after it has failed inresponse to tensile force and further showing the reduction in diameterof the tube.

FIG. 8 is an elevation in cross section of an alternate form of theinvention.

FIG. 9 is a view of the form of the invention of FIG. 8 immediatelyafter the tube has failed in response to tensile forces.

FIG. 10 is a sectional view of another alternate form of the invention.

FIG. 11 is a sectional view of still another alternate form of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring more particularly to the drawings and to FIG. 1, whichillustrates one exemplary environment in which the invention finds use,there is a steam boiler assembly B within which a water drum W ismounted in the lower region of the boiler and a steam drum S is locatedin the upper region of the boiler. Extending between water drum W andsteam drum S is a plurality of boiler tubes T. The region within boilerB exterior of tubes T is typically filled with flame, and waterintroduced to water drum W flows through the tubes and is converted bythe flame to steam which is collected in steam drum S. Water drum W andsteam drum S are typically relatively thick-walled members and have avirtually unlimited life. In contrast, tubes T are relativelythin-walled and because they are subjected to extremely hightemperatures during use, have a relatively limited life. Conventionalpractice is to replace tubes T periodically, and the present inventionis adapted to facilitate such replacement.

The fit between the external surface of tubes T and the passages in thewalls of the water and steam drums is an extremely tight one. Thetightness arises because during installation of the tubes in the drumwall passages, the tubes are expanded, and because over the course oftime, the extreme temperatures present within the structure contributefurther to the tightness. Of extreme importance when spent tubes areremoved is avoidance of damage to the walls that define the passages inthe drum walls. A known technique for effecting removal of the tubeswithout damaging the drum wall passages is to fix one end of the tube,insert a tube gripper into the other end, and apply tensile force to thegripper. As the tube stretches prior to failure, its diameter contractsso that on failure, the tube is parted without abrading the wall thatdefines the passage in which the tube resides. This technique isimpracticable, however, where space for installation of the clamp islimited.

In removing boiler tubes as described above it is essential that one endof the tube be firmly fixed with respect to the boiler wall. Typicalprior art practice involves using two workers, one on each side of aboiler wall. The worker who will ultimately do the pulling is stationedon the proximal side and the worker who will attend to fixing theopposite end of the tube is deployed on the distal side. Such practiceis not only inefficient but can be extremely difficult for one or theother worker where space is limited or access is impossible.

In the foregoing introductory remarks regarding the environment in whichthe present invention finds particular application, the specification ofa boiler is only by way of example because the invention findsapplication in any environment where tubes must be removed from tightengagement with a passage through a member. For example, heat exchangershave tube sheets which coact with the tubes installed therein in amanner analogous to that described above in connection with boilers. Inthe ensuing discussion the use of the term boiler wall should beconstrued as the equivalent of a heat exchanger tube sheet or any solidbody that defines a passage in which a tube is tightly disposed and fromwhich the tube is to be removed without damaging the surface of thepassage.

Referring to FIG. 2, a fragment of a boiler wall is indicated at W'. Atube T is tightly installed within a passage formed in wall W'. At theleft-hand end of the wall fragment as viewed in FIG. 2, referred tohereinafter as the proximal side of the wall, the tube is flared asindicated at 12. Tube T at the opposite or distal side extends to someother similar wall in the manner shown in FIG. 1. According to theinvention there is a jaw assembly 14, the details of which are describedhereinbelow, which can be retracted to a diameter such as to passthrough tube T from the proximal side of wall W'. A jaw expander 16extends through the interior of jaw assembly 14 and coacts with the jawassembly to expand the jaws outward into engagement with the interior oftube T. Adapted for engagement with the expander is a tapered mandrel 18which has a length sufficient to afford retraction of that jaw assembly14 so that the jaw assembly can be positioned within tube T.

A hollow reaction tube 20 is provided. The reaction tube has an insidediameter sufficient to afford the free passage of mandrel 18therethrough and a length sufficient to extend through the passage inwall W' and bear against the end of jaw assembly 14; the reaction tubedefines an annular abutment surface 22 for the latter purpose. The endof reaction tube 20 opposite the annular abutment surface is externallythreaded at 24. A retaining nut 26 has an internally threaded bore 28adapted for threaded engagement with the threaded portion 24 of thereaction tube. Retaining nut 26 also defines an annular abutment surface30 adapted to bear against the proximal surface of wall W'. The innerdiameter of annular abutment surface 30 is sufficient to clear flare 12of the boiler tube. Extending radially to the inner surface of threadedbore 28 is a set screw 32 which is employed to lock the retaining nut tothe reaction tube at a position such that when annular abutment surface30 rests against the proximal surface of boiler wall W', contact betweenreaction tube abutment surface 22 and jaw assembly 14 positions the jawassembly in alignment with the distal surface of the boiler wall. Astraight mandrel 34 is provided with a longitudinally extendinginternally threaded opening 36 for engagement with complemental threadson mandrel 18. The opposite end of straight mandrel 34 is engaged with acommercially available pulling mechanism 40 which forms no part of theinvention. Suffice it to say for the present disclosure, pullingmechanism 40 is typically hydraulically powered so as to draw mandrel 34outward (to the left as viewed in FIG. 2), in respect to an extensionsleeve 42 which bears against the end of retaining nut 26 opposite fromannular abutment surface 30 so as to keep the retaining nut and reactiontube 20 in place as tensile force in the leftward direction on mandrel34 is applied by the mechanism.

As can be seen in FIGS. 2 and 6, jaw assembly 14 includes foursubstantially identical segments 14a, 14b, 14c, and 14d. The segmentsare circumferentially limited so as to afford movement of the segmentsto a retracted position at which the jaw assembly can be introducedinteriorly of tube T. The segments have tapered exterior surfaces onwhich are formed sharp ridges 43 (FIG. 3) so that as the jaws areexpanded, the ridges deform the inner surface of the tube and providefirm engagement between the jaw assembly and the tubes. The exteriorsurfaces of the jaw segments are also formed with a circumferentialgroove in which an elastic retaining ring 44 is disposed. The retainingring serves to retain the jaw segments in assembled condition on jawexpander 16 and tapered mandrel 18.

Installation of one device constructed in accordance with the inventionwill be described in connection with FIG. 3 and the use of the devicewill be described in connection with FIGS. 4-7. In FIG. 3 jaw assembly14 is seen in a retracted position at which the outer dimension of theassembly is such as to afford insertion from the proximal side throughthe interior of the tube to a position at which the jaw assembly is atthe distal side of wall W'. To so establish such position of the jawassembly, retaining nut 26 is threaded along threaded portion 24 ofreaction tube 20 so that when the annular abutment surface of thereaction tube, the rightward extremity as viewed in FIG. 3, bearsagainst jaw assembly 14 and abutment surface 30 of nut 26 bears on theproximal surface of the wall, the jaw assembly is positioned correctly.The relative position of retaining nut 26 and the reaction tube ispreserved by tightening set screw 32 after the correct position has beenestablished. Before insertion of the apparatus into tube T, jaw expander16 is threaded onto tapered mandrel 18 at a threaded joint 46. Also,mandrel 18 is threaded into pulling mandrel 34 at a threaded joint 48.For reasons described below, the threads are of opposite sense.

Jaw assembly 14 is positioned toward the relatively small diameter oftapered mandrel 18 so that the jaw assembly resides in the retractedposition at which the outermost dimension of the jaw assembly is lessthan the inner diameter of tube T. The apparatus can then be introducedinto tube T to the position seen in FIG. 3. Next, tension applyingmechanism 40 is coupled to the apparatus and is activated. The mechanismapplies a relative force between the parts indicated by an arrow 50'which tends to position retaining nut 26 against the proximal surface ofthe wall so as to hold jaw assembly 14 in the correct position and anarrow 52' which draws expander 16 into the complementally taperedcentral core of jaw assembly 14 so as to cause expansion of the jawsegments of the assembly. Ultimately, the jaws are expanded to theposition seen in FIG. 4 after jaw assembly actuator 16 has been drawnsufficiently into the central tapered bore of jaw assembly. As seen inthe latter figure, the walls of tube T are expanded outward so that tubeT at the distal wall surface has an outside diameter greater than theinside diameter of the passage through wall W'. At such position,movement of the tube within the wall passage toward the distal side ofthe wall is virtually impossible. Next, a suitable turning tool isattached to the accessible end of pulling mandrel 34 and the mandrel isrotated in a direction to unthread the connection at threaded portion46. Because threads 48 are formed at an opposite sense, such rotation ofthe pulling mandrel avoids disengagement of those threads.

After pulling mandrel 34 and tapered mandrel 18 have been removed, jawassembly 14 and jaw assembly expanded 16 reside in the position seen inFIG. 4, a position at which the jaw assembly is substantially confinedadjacent the distal extremity of the passage and at which the remainderof the interior of tube T is accessible. The degree of taper of theinternal opening of jaw assembly 14 and the external surface of jawexpander 16 are such as to form a sticking taper. In this context asticking taper means a taper that satisfactorily expands the individualjaw segments of the jaw assembly when the expander is moved in aleftward direction as viewed in the drawings and will remain in thatposition after the tension is removed from pulling mandrel 34 andtapered mandrel 18. In one apparatus designed in accordance with theinvention an included angle of about six degrees has been found toafford the requisite sticking taper.

With the distal extremity of the tube fixed as described above, threadedengaging tool 49 is installed in the interior of tube T from theproximal end thereof. The tool, a known article of commerce, is oftap-like configuration so that it can cut threads on the internalsurface of tube T as it is rotated thereinto. After the tool 49 isfirmly engaged to the inner wall of tube T, tension applying mechanism40 is connected to draw the tool and the portion of tube T within theboiler wall passage outward in the direction of the arrow seen in FIG.7. As the force is continued, the portion of tube T within the wallpassage begins to elongate or stretch and in doing so effects areduction in diameter. By the time the tensile force applied to the tubeexceeds the strength of the material of which the tube is made, theouter diameter of the tube within the wall passage is reduced so that onfailure of the tube, seen in FIG. 7, contact between the outer tubesurface and the wall passage is virtually non-existent in consequence ofwhich the tube is removed without adversely affecting the passagesurface.

Upon failure of the tube and removal of tension applying tool 40 and thepart of the tube at the left, as viewed in FIG. 7, tapered mandrel 18and straight mandrel 34 are reinstalled so that the tapered mandrel isengaged with jaw expander 16 at threaded joint 46. Then inward force onthe mandrels and the jaw expander is applied to move the jaw expanderrightward as viewed in FIGS. 3, 4, 5, and 7 and out of engagement withjaw assembly 14. This permits the energy stored in elastic retainingring 44 to move jaw segments 14a-14d to a retracted position free of theinner surface of tube T, after which the mandrels 18 and 34, jawassembly 14, and jaw expander 16 can be removed from the distal side ofwall W'.

In the usage of the invention described immediately above and as seenmost clearly in FIG. 3, tube T is flared at 12 and the inner diameter ofthe opening in retaining nut 26 is sufficient to clear the flare so thatannular abutment surface 30 of the retaining nut can bear against thewall at the proximal end of the tube passage. There are manyinstallations of boilers, heat exchangers, and like apparatus whererelatively convenient access can be had to the side of the wall at whichthe flare 12 is present. In certain installations, however, access tothe side of the wall at which the tube flare exists in less convenientthan access to the other side. For example, there are certain highlycompact installations where access to the flared side can be had onlythrough hand holes which are not necessarily aligned with the tube topermit extraction of the tube as has been described previously inconnection with FIGS. 3-7. Modifications of the invention permitutilization of the invention in such compact installations.

Referring to FIG. 8, a wall such as a boiler wall is indicated at W'.Spaced from the side of the wall at which tube flare 12 is positioned isa second wall 50 which contains hand holes or inspection ports one ofwhich is shown at 52. Hand hole 50 is covered by a removable cover 54during usage of the boiler or heat exchanger of which it is a part; thecover 54 can be removed during maintenance. Because many of the parts ofthe embodiment of the invention of FIG. 8 are similar to those referredto previously, reference numerals greater by 100 than those previouslyused are employed in FIG. 8. There is a jaw assembly indicated at 114with which a jaw expander 116 coacts. For threaded connection withexpander 116 is a tapered mandrel 118 which in turn is adapted forthread engagement with a pulling mandrel 134. A reaction tube 120 has athreaded portion 124 with which a retaining nut 126 is engaged.

The specific configuration of jaw assembly 114 is different from thatpreviously described in that its outer extremity is provided with abeveled shoulder 56 opposite sides of which include an angle such as toengage the inner surface of tube flare 12 and effect firm retention anddeformation or partial flattening of the flare against the distalsurface D of the wall in which tube T is installed.

In using a device of the form exemplified by FIG. 8, jaw assembly 114and jaw expander 116 are assembled and manually held in an assembledcondition by a worker positioned at the external side, the left-handside as viewed in FIG. 8, of wall 50. The worker then introduces the jawassembly and expander through inspection port 52 into position at whichtapered surface 56 rests against tube flare 12. The outer axialextremity of expander 116 is provided with a non-circular opening 58,such as a hexagonal shaped opening, so that the worker on the outer sideof wall 50 can prevent the expander from rotating by engagement with anAllen wrench or the like shown in broken lines at 60. Another workerstationed at the proximal surface of wall W', after having first severedthe portion of tube T indicated by broken lines in the figure,introduces tapered mandrel 118 and tension mandrel 134 into the centralopening of the tube. Then engagement of threaded connection 148 isachieved by cooperation of the persons positioned as describedimmediately above. Thereafter, tension is applied to tension mandrel 134to effect expansion of jaw assembly 114 and fixing of the distalextremity of tube T after which removal of pulling mandrel 134 andtapered mandrel 118 are effected by unthreading the structure atthreaded connection 146.

As described previously in connection with FIGS. 3-7, threaded engagingtool 49 is introduced to the interior of tube T and the same steps arerepeated to extract the tube from the passage in wall W' withoutadversely affecting the integrity of the surface that defines thepassage. After removal of the main portion of the tube, the portionadjacent the tube flare 12 and jaw assembly 114 and jaw expander 116 canbe tapped loose without damage to the passage defining the opening inwall W'.

A further modification illustrating the advantages of the invention isshown in FIG. 10 in which equivalent structures are identified byreference numerals 100 greater than those employed in FIGS. 8 and 9. Themodification of FIG. 10 includes a jaw assembly 214 in which the outerextremities of the jaw segments have outwardly extending flaredshoulders 62 which form a substantially annular bearing surface 64 onthe inner end of the shoulders. A reaction cap 66 is provided with amajor inner opening 68 having a diameter sufficiently large to cleartaper 12 on tube T. Inward of opening 68, retainer 66 is provided with acylindric shape undercut 70 which defines an annular bearing surface 72adapted to cooperate with bearing surface 64 on jaw assembly 214 toprevent longitudinal movement of the jaw assembly in a manner analogousto the function of reaction tube 20 referred to previously in connectionwith description of the embodiment of FIGS. 1-7.

As in the embodiment described in connection with FIGS. 8 and 9, theembodiment of FIG. 10 is installed by preliminarily assembling tubeexpander 216, tapered mandrel 218, and retainer 66. Installationprogresses as described in connection with FIG. 8, a non-circulargripping member 158 being provided in jaw expander 216 so as to permitengagement of the pulling mandrel, equivalent to that identified at 134in FIG. 8, so that pulling can proceed. Retainer 66 is provided with anopening 74 for affording access to the non-circular gripping member injaw expander 21. Because of the coaction between abutment surface 64 onthe jaw assembly and abutment surface 72 on the retainer, jaw assembly214 is confined solely to radial movement during expansion thereof.Expansion affords a firm engagement between the teeth on jaw assembly214 and the inner wall of tube T and partial deformation of tube flare12 so that upon unthreading of tapered mandrel 218 at a threaded joint246, the interior of tube T is accessible for introduction of threadedgripping tool 49 and removal of the tube as previously described.

The modification seen in FIG. 11 achieves the advantages of that seen inFIG. 10 without the necessity for retainer 66. In FIG. 11 is seen a jawassembly 314 on the outer end of which is an integral outward extendingflange 76. Rigid with or integral with the flange is an annular ring 78having a bearing surface 80 adapted to bear on the distal surface of thewall in which a tube to be removed is installed. The construction of theexpander used in connection with the embodiment of FIG. 11 issubstantially identical to that seen in FIG. 10 except for theelimination of a separate reaction member. Because the installation anduse of the embodiment of FIG. 11 is virtually identical to thatdescribed in connection with FIG. 10, no further description of same isneeded here.

In the embodiments described herein, the external ridged surface of jawassembly 14 of FIG. 3 (and its counterparts in the other figures) istapered, the proximal end of the ridged surface having a diametersmaller than that of the distal end of the surface. This configurationfunctions to assure good engagement by the smaller diameter end with theinternal surface of the tube and to assure that the portion of the tubebeyond the distal surface of the wall in which the tube resides isexpanded so the outer diameter of the tube exceeds the inner diameter ofthe wall passage from which the tube is to be extracted.

Thus, it will be seen that the present invention provides apparatus forexpediting removal of boiler tubes without jeopardizing the surface ofthe passage in which the tube is installed. This is achieved because theinvention affords apparatus for fixing the tube at the distal surface ofthe wall in which it resides so that a worker positioned at the proximalsurface of the wall can effect extraction of the tube as has beendescribed. Not only does use of the invention reduce or eliminate damageto the wall passage in which the tube is installed, it materiallyexpedites removal of the tube.

Although several embodiments of the invention have been shown anddescribed, it will be apparent that other adaptations and modificationscan be made without departing from the true spirit and scope of theinvention.

What is claimed is:
 1. Apparatus for fixing one end of a tube thatdefines a fluid path centrally thereof within a passage in which thetube is tightly disposed, the passage having a proximal extremity and adistal extremity between which the tube extends, comprising a jawassembly having at least three jaw segments and being movable between aretracted position at which the outer dimension of the jaw assembly canbe inserted into the tube path and an expanded position at which theouter dimension of the jaw assembly exceeds the tube path dimension,retaining means for resiliently retaining the jaw segments in theretracted position to afford insertion of the jaw assembly within thetube path at the distal extremity, said jaw assembly having expansionmeans interior thereof for effecting movement of said jaw segments tothe expanded position, and actuating means extensible through thecentral tube path beyond the proximal extremity for actuating saidexpansion means, said actuating means being disengagable from saidexpansion means to afford substantially unrestricted access to theproximal extremity of said tube when said jaw assembly is in theexpanded position at said distal extremity, said expansion meanscomprising an opening extending through said jaw assembly, said openingbeing tapered in a direction that converges toward said proximal end,said actuating means including an expander having an external surfacethat is tapered in correspondence to said jaw assembly opening so thatmovement of said expander toward said proximal end effects expansion ofsaid jaw segments.
 2. Apparatus as claimed in claim 1 wherein saidactuating means includes a first member disposed in threaded engagementwith said expander in axial alignment therewith, the threads of thethreaded engagement between said first member and said expander being inone direction, and a second member disposed in threaded engagement withsaid first member in axial alignment therewith, the threads of thethreaded engagement between said first and second members being in anopposite direction with respect to the threaded engagement between saidfirst member and said expander, whereby said second member is adaptedfor exerting a pulling force on said first member to move said expandertoward said proximal end while said first member and said expander arein threaded engagement, and said first member is adapted to bedisengaged from said expander for removing said first and second membersfrom said central tube path.
 3. Apparatus for fixing one end of a tubethat defines a fluid path centrally thereof within a passage in whichthe tube is tightly disposed, the passage having a proximal extremityand a distal extremity between which the tube extends, comprising a jawassembly having at least three jaw segments and having a firstrelatively small diameter end and a second end remote from said firstend that has a diameter larger than the diameter of said first end, saidjaw segments being movable between a retracted position at which saidfirst end can be introduced into said tube at the distal extremitythereof expanded position at which said first end radially stresses saidtube in an outward direction, said second end residing externally ofsaid tube at the distal extremity of said tube to prevent movement ofsaid tube in a proximal direction in response to force applied to saidtube in a proximal direction, means operable through said tube from saidproximal end for effecting expansion of said jaw assembly from theretracted position to the expanded position, said second end of said jawassembly defining a shoulder that extends outward of said jaw assemblyand defining a bearing surface that faces said first end of said jawassembly, and a retainer having a surface for bearing on the margin ofsaid passage, said retainer defining a centrally extending opening forreceiving said second end of said jaw assembly therein, said retainerhaving in said opening an undercut for receiving said shoulder therein,said undercut defining a distally facing annular bearing surfacecooperable with said shoulder bearing surface to prevent longitudinalmovement of said jaw assembly toward said proximal extremity. 4.Apparatus for fixing one end of a tube that defines a fluid pathcentrally thereof within a passage in which the tube is tightlydisposed, the passage having a proximal extremity and a distal extremitybetween which the tube extends, comprising a jaw assembly having atleast three jaw segments and having a first relatively small diameterend and a second end remote from said first end that has a diameterlarger than the diameter of said first end, said jaw segments beingmovable between a retracted position at which said first end can beintroduced into said tube at the distal extremity thereof and expandedposition at which said first end radially stresses said tube in anoutward direction, said second end residing externally of said tube atthe distal extremity of said tube to prevent movement of said tube in aproximal direction in response to force applied to said tube in aproximal direction, means operable through said tube from said proximalend for effecting expansion of said jaw assembly from the retractedposition to the expanded position, said second end of said jaw assemblydefining an outward extending flange rigid with said jaw assembly, saidflange having a diameter greater than the diameter of said passage and asurface facing the first end of said jaw assembly, and spacer meansrigid with said flange and extending from said surface to space saidsurface distally of the distal extremity of said passage, said spacermeans defining a central opening larger than the outer diameter of saidtube so as to define a clearance space for a portion of the tubeextending beyond the distal extremity of said passage.
 5. Apparatus forfixing one end of a tube that defines a fluid path centrally thereofwithin a passage in which the tube is tightly disposed, the passagehaving a proximal extremity and a distal extremity between which thetube extends, comprising a jaw assembly having at least three jawsegments and being movable between a retracted position at which theouter dimension of the jaw assembly can be inserted into the tube pathand an expanded position at which the outer dimension of the jawassembly exceeds the tube path dimension, retaining means forresiliently retaining the jaw segments in the retracted position toafford insertion of the jaw assembly within the tube path at the distalextremity, said jaw assembly having expansion means interior thereof foreffecting movement of said jaw segments to the expanded position, andactuating means extensible through the central tube path beyond theproximal extremity for actuating said expansion means, said actuatingmeans being disengagable from said expansion means to affordsubstantially unrestricted access to the proximal extremity of said tubewhen said jaw assembly is in the expanded position at said distalextremity, said tube being connected to a wall having a proximal surfaceand a distal surface, said apparatus comprising a threaded tubesurrounding said actuating means and arranged to abut against said jawassembly, a threaded guide member disposed in threaded engagement withsaid threaded tube and having an abutment surface for engagement withthe proximal surface of said wall for positioning said jaw assembly inalignment with the distal surface of the wall.